The Use of Levers and Pedals in Wheel Loaders - Frequency and Duration

Abstract

Working in terrain vehicles may cause muscnloskeletal disorders. These disorders mainly arise from static and often inappropriate working postures together with vibrations. In Sweden, operators of wheel loaders are exposed to the working environment in these machines for an average of 1500 hours per year.The hip and knee angle has been shown to influence lumbar lordosis. Sitting in a higher sitting position, such as saddle seats, has been shown to decrease the kyphosis of the spine compared to sitting on a conventional seat. In recently published ergonomic guidelines for forest machines (Fnnnerie, 1999) it is recommended that the driver should have the possibility to vary the trunk-thigh angle between 105" and 120" and to be able to bend the knees and place the feet under the seat. Therefore, a large project has been initiated with the aim of investigating how levers and pedals should be placed and designed in an ergonomically appropriate way when sitting in these new working postures driving wheel loaders.This study forms one part of the larger project described above. The purpose of this study was to investigate the duration and frequency of activating the right-hand levers and the foot pedals in today's wheel loaders.By means of potentiometers, the positions of the right-hand levers were measured continuously when driving. The activation of each lever was classified into five zones: full turn forward, half turn forward, neutral, half turn backward and full turn backward. The neutral zone varied between different machines depending on the free play in the levers. The activation time was classified into four periods: ~0.4 set, 0.4-1.2 set, 1.2-5 set and >5 sec. The lever activation was analysed with Exposure Variation Analysis (Mathiassen, 1993). The activation of the foot pedals was recorded by micro switches, measuring only the on-off activation.The driver was also video recorded by three cameras, one recording the movement of the right hand, one recording through the front window and one recording the movement of the machine from outside the cab. The video cameras were used in order to define and analyse work cycles during the work. So far, one task with the use of bucket has been investigated. It consisted of short cycles when loading a truck and trailer with aggregate. Twelve regular work cycles were analysed. The mean cycle time was 41 set with a standard deviation of 3 sec. Filling the bucket took 19 % and emptying took 17 % of the cycle time. Transporting (moving the wheel loader from one point to another) took 63 % of the work cycle.The lift lever was activated 81 % and the tilt lever 55 % of the cycle time. At least one lever was activated during 90 % of the cycle time and both levers were activated simultaneously 46 % of the cycle time. The lift lever was activated on average 6 times/minute and the tilt lever 5 times/minute. The lift lever was mainly activated during 1.2-5 set and the tilt lever more than 1.2 sec.The driver used only the left foot brake. The duration when activating the accelerator w...